The present invention relates to pneumatic brake boosters of the type comprising a housing formed from two front and rear half-shells, a piston structure dividing the housing internally into two chambers and composed of an assembly consisting of a plate and of a diaphragm and possessing centrally a hub structure containing a distribution valve means actuable by an input member in order to generate a pressure difference selectively between the chambers, the valve means comprising a plunger mounted axially slideably in a central bore of the valve body and connected to the input member, the plunger defining a first shutter seat at one of its ends, a second shutter seat being formed in the valve body concentrically relative to the first shutter seat and a shutter means mounted in the valve body and stressed elastically towards the first and second shutter seats, at least one elastic means stressing the input member axially away from the shutter seats.
Boosters of this type are well known in the prior art.
In conventional pneumatic boosters, the hub structure is composed of an integral solid piece which contains the distribution valve means and a tubular part of which extends rearwards on the outside of the housing, so as to receive an input rod intended to be connected to a brake pedal.
This conventional arrangement functions satisfactorily. However, such a design has various disadvantages. First of all, the presence of the rear "chimney" contributes to making the booster heavier, whereas the manufacturers' aim is to lighten the weight of motor vehicles as much as possible. Furthermore, this chimney gives the booster a large overall size, whilst the space available in the engine compartment is increasingly limited. Finally, manufacturers want to automate the assembly of motor vehicles as far as possible. Various solutions have therefore been proposed for the robotized mounting of boosters having a chimney by way of the engine compartment, but most of the time they require a prepositioning of an accuracy higher than the current performances of assembly robots.